Green function of a radial current in a circular waveguide with a short-circuiting plunger is derived

and the electric field radiated by the currents on the radial cylindrical probe is calculated. When the dominant mode TE11 is propagated alone in the circular waveguide

the input impedance and higher order mode reactance may be determined by applying the complex Poynting vector to the coaxial-line opening. Formulae and curves are given for obtaining the optimum design of the feed. An example showing how the feed is-designed is presented in the frequency band of 8

400MHz

1

0

600MHz

with VSWR≤1.27. The theoretical calculation is in good agreement with experimental results.